Lignin is a biopolymer composed of a complex group of phenolic polymers that confer strength and rigidity to woody cell walls of various plants. The lignin is typically chemically recovered from the plants by various methods, including recovery as paper pulp byproducts. Lignin is typically required to be removed from wood pulp when the wood pulp is to be used for making paper. It can therefore be a byproduct from paper making processes, although lignin can be recovered by other processes.
In practice, lignin may be recovered from wood pulp by various processes such as for example, by solvent extraction from wood meal, which may sometimes be referred to as “Native Lignin” or “Brauns Lignin”; by cellulolytic enzyme treatment of finely ground wood meal followed by solvent extraction, which may sometimes be referred to as “Cellulolytic Enzyme Lignin”; by treatment of woody material with dioxane/dilute HCl, where come linkages are cleaved by such procedure, thus altering the lignin structure, which may sometimes be referred to as “Doxane Acidolysis Lignin”; by solvent extraction and purification of finely ground wood meal, which may sometimes be referred to as “Milled Wood Lignin”; by strong acid degradation of woody materials which is understood to drastically change the lignin structure which may sometimes referred to as “Klason Lignin”; by successive treatments of woody material with sodium periodate followed by boiling water, where the lignin is degraded in some degree, which may sometimes referred to as “Periodate Lignin”; by reaction with sodium hydroxide and Na2S at an elevated temperature followed by isolation through acidification or ultrafiltration. The resulting product (a byproduct of paper pulp making process) is water insoluble although it may be in a sulfomethylated, water soluble, form. It may sometimes be referred to as “Kraft Lignin”; by reaction with sulfur dioxide and metal bisulfite in an acidic medium and at an elevated temperature. The resulting water soluble lignosulfonates may contain sulfonated lignin polymers, sugars, sugar acids and small amounts of wood extractives and inorganic compounds. The product may be submitted to a purification process or chemical reaction to obtain the lignin. This may be one of the largest commercial sources of lignin. It may sometimes be referred to as “Lignosulfonates—from Acid Sulfite Pulping”.
Other less significant sources of lignin are, for example, treating woody material with a metal bisulfite salt at an elevated temperature to yield a water soluble product containing 40 to 50 percent sulfonated lignin with the remainder being composed of sugar polymers, sugars, sugar acids, wood extractives and a significant inorganic compound content. They might sometimes be referred to as “Lignosulfonates from Bisulfite Pulping”; by treating woody material with a salts of bisulfite/sulfite prior to mechanical refining. The resulting water soluble product contains relatively low yields of lignin itself together with a variety of degradation products. It might sometimes be referred to as “Lignosulfonates from Neutral Sulfite-Semi Chemical Process”; by treatment of woody material with sodium sulfite and catalytic amount of anthraquinone at an elevated temperature. An impure yield of sulfonated lignin is obtained. While believed to not be a commercial product, it might, if desired, be referred to as “Lignosulfonates from Alkaline Sulfite-Anthraquinone Pulping”; by treatment of woody material with various organic solvent treatment processes which may result in a high percentage of purified lignin. The might, if desired, be referred to as “Organosolv Lignins”.
For the purposes of this invention, such lignin products may be collectively referred to herein as “lignin” or “lignins”.
While lignin, as a byproduct of various processes, may sometimes be disposed of by, for example, use as a fuel, lignin may sometimes find use for other purposes. For example, lignin has sometimes been suggested for use as a filler for various rubber compositions.
In practice, lignin is generally considered to be a biopolymer composed of several phenolic monomers in various ratios and in various configurations, depending somewhat upon its plant of origin and process used for its recovery. These aspects of lignin are recognized by those having skill in such art.
Accordingly, the nature of an individual lignin depends somewhat upon its plant of origin and recovery process.
Lignin is understood to generally and predominately contain, aromatic, hydroxyl, methoxyl, carbonyl and carboxy groups, or substituents. Lignosulfonates may also contain sulfonate moieties, or substituents.
For the purposes of this invention, such substituents may be collectively referred to herein as “resident substituents”. It can be envisioned that most of such substituents are composed of chemically active hydroxyl groups.
For this invention, it is desired to functionalize the lignin through one or more of its various chemically active resident substituents, particularly those involving chemically active hydroxyl groups, with at least one functional group having a moiety reactive with at least one of such resident substituents.
For the purposes of this invention, such functionalized lignin may be referred to herein as “functionalized lignin”.
It is envisioned herein that such functionalized lignin may be obtained, for example by esterification to form lignin ester and by silylation to form silylated lignin.
Further, it is envisioned herein that lignin may alternatively be provided in a form of digested lignin prior to its functionalization. Said digested lignin may be functionalized, for example, by esterification or silylation.
Digested lignin may be prepared by, for example, by treatment of lignin with a protic acid, such as for example, sulfuric acid, in order to digest the lignin to promote smaller sized lignin particles having an average particle size ranging from, for example, about 40 nanometers (nm) to about 1,200 nm. Such treated lignin may be referred to herein as “digested lignin”.
In one aspect, it is proposed to provide such functionalized lignin to promote its use as a filler for reinforcement of elastomers. In another aspect, it is desired to provide such functionalized lignin as a reinforcing filler to promote replacement of at least a portion of rubber reinforcing fillers in a rubber composition, such as for example, rubber reinforcing carbon black.
It is further proposed to provide a product which contains at least one component of a rubber composition which contains such functionalized lignin. Representative of such products are, for example, tires and engineered products such as hoses, conveyor belts, transmission belts and shock absorbing elements for various purposes.
In the description of this invention, the term “phr” relates to parts by weight for a material or ingredient per 100 parts by weight elastomer(s)”. The terms “rubber” and “elastomer” are used interchangeably unless otherwise indicated. The terms “cure” and “vulcanize” are used interchangeably unless otherwise indicated.